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Prisms

Prisms play an important role in optical instrument, though new technolgies such as
digital image reduce the need of prism in morden optical instrument.
Prisms are used to bend a light to a specific angle either by deflection, reflection
(total internal reflection) or both. Simple prisms are named by prism's geometric shape
such as right angle prism, penta prism, roof prism, etc. Complicate prisms are named
to the designer, such as Abbe prism, Pellin-Broca prism, Bauernfeind prism and so on.

1. Reflective Prisms

Reflective prisms are used to reflect a light, in order to flip, invert, rotate,
deviate or displace a light beam. They are typically used to erect the image
in binoculars or single-lens reflex cameras - without the prisms, the image
would be upside down for the user. The most common reflective prisms are:

2. Dispersive Prisms

Dispersive prisms are used to break up light into its constituent spectral colors.
Because the refractive index depends on frequency, the white light entering
the prism is a mixture of different frequencies, each of which gets bent slightly
differently. Blue light is slowed down more than red light and will therefore
be bent more than red light:

3. Deflecting Prisms

Wedge prisms are used to deflect a beam of light by a fixed angle. A pair of
such prisms can be used for beam steering; by rotating the prisms the beam can
be deflected into any desired angle within a conical "field of regard".
The most commonly found implementation is a Risley prism pair.

5. Compound Prisms

In advanced imaging system, different color light are separately imaged into
three or more CCD/CMOS sensors. The RGB(Philips) prism is designed to split white
light into RGB colors. Philips prism is well suitable for reflective LCOS Projector,
matrix camera applications.